This invention relates to the reactions of hydroxyaromatic compounds, and more particularly to the conversion of such compounds to brominated derivatives, monocyclic dihydroxyaromatic compounds and dihydroxybiphenyls.
Monocyclic dihydroxyaromatic compounds such as hydroquinone and dihydroxybiphenyls such as 4,4′-dihydroxybiphenyl (hereinafter sometimes simply “biphenol”) have numerous uses in the chemical industry. For example, both compounds can be used in polymer preparation, notably in the preparation of polycarbonates, polysulfones and polyimides, especially polyetherimides.
There are various methods for the preparation of hydroquinone and biphenol. As examples of such methods, each compound can be prepared from p-bromophenol, hydroquinone by hydrolysis and biphenol by reductive coupling in the presence of a noble metal catalyst, a base and a reducing agent.
Brominated hydroxyaromatic compounds, as exemplified by p-bromophenol, can be prepared by reaction of the precursor hydroxyaromatic compound with elemental bromine or with various kinds of bromides. For the most part, the use of hydrogen bromide alone is not successful. Auxiliary reagents are required; these may include oxidizing agents, reducing agents, catalysts and/or complexing agents. As a result, the commercial production of bromophenols by reaction of phenols with hydrogen bromide or other simple ionic bromides has, in general, not been pursued.
Normally, chemical plants are set up to produce a single product or group of products in a single reaction or a unitary sequence of reactions. It is thus possible to set up a single set of equipment and use it, on either a batch or continuous basis, permanently to produce the desired product.
Toll producers of chemicals, on the other hand, may utilize a wide variety of equipment, choosing individual items for use depending on the chemical then being produced. To vary the product, they may vary the reactors employed and/or the connections between reactors so as to design a suitable set of equipment for the particular product.
So far as is presently known, the use of a unitary set of equipment to produce two or more widely diverse products is not a commercial alternative.